1. Field of the Invention
The present invention relates to a device for use in tubing expansion and to methods of expanding tubing. In particular, but not exclusively, embodiments of the present invention relate to devices and methods for use in expanding tubing downhole.
2. Description of the Related Art
In the oil and gas exploration and production industry, bores drilled to access subsurface hydrocarbon-bearing reservoirs are lined with tubing, known as casing and liner. Furthermore, strings of tubing may be located within the cased bore to, for example, carry production fluid to surface. Recently, there have been numerous proposals to use tubing which is expanded downhole, that is tubing of a first diameter is run into a bore and then expanded to a larger second diameter. This offers many advantages to the operator, primarily providing the ability to create lined bores which do not necessarily suffer a loss in internal diameter each time a string of tubing is located in the bore, beyond an existing section of tubing-lined bore.
Early proposals for expanding tubing downhole featured the use of cones or mandrels, which are driven through the tubing in order to expand the tubing. Other proposals include the use of roller expanders, some of which feature radially-urged rollers.
When tubing is expanded using a cone or mandrel, the expansion mode is different from when tubing is expanded using roller expanders. Typically, tubing expanded with a cone or mandrel tends to shorten in axial length whilst maintaining or suffering only a small reduction in wall thickness. Tubing expanded using roller expanders, however, tends to extend in axial length and experiences a reduction in wall thickness, caused by a wall thinning action.
These two different types of expansion devices offer various advantages and disadvantages depending upon the particular circumstances in which the device is employed.
Also, it is generally preferred to expand tubing in a top-down expansion procedure, as it is possible to recover the expansion device in the event that the tool becomes lodged in the tubing. However, when expanding tubing using an expansion cone or mandrel, it is conventional to employ a bottom-up expansion procedure. This is because it is necessary to apply a relatively large force on the cone from surface (by setting weight down on the cone), or to apply a relatively high pressure to the reverse face of the expansion cone (such as by supplying a pressurised fluid behind the cone), and it is not possible or safe to achieve the required loading or pressure on the cone in a top-down expansion procedure. This is particularly true for deviated (horizontal) wells and extended reach wells, where the forces required to expand tubing are, generally speaking, relatively high.
It is amongst the objects of embodiments of the present invention to provide improved devices and methods for use in expanding tubing downhole.